Bottom Line:
Our system is based on a digital neuromorphic chip consisting of 256 leaky-integrate-and-fire neurons, 1024 × 256 crossbar synapses, and address-event representation communication circuits.The neural circuits configured in the chip reflect established connections among mitral cells, periglomerular cells, external tufted cells, and superficial short-axon cells within the olfactory bulb, and accept input from convergent sets of sensors configured as olfactory sensory neurons.Our circuits, consuming only 45 pJ of active power per spike with a power supply of 0.85 V, can be used as the first stage of processing in low-power artificial chemical sensing devices inspired by natural olfactory systems.

ABSTRACTWe present a biomimetic system that captures essential functional properties of the glomerular layer of the mammalian olfactory bulb, specifically including its capacity to decorrelate similar odor representations without foreknowledge of the statistical distributions of analyte features. Our system is based on a digital neuromorphic chip consisting of 256 leaky-integrate-and-fire neurons, 1024 × 256 crossbar synapses, and address-event representation communication circuits. The neural circuits configured in the chip reflect established connections among mitral cells, periglomerular cells, external tufted cells, and superficial short-axon cells within the olfactory bulb, and accept input from convergent sets of sensors configured as olfactory sensory neurons. This configuration generates functional transformations comparable to those observed in the glomerular layer of the mammalian olfactory bulb. Our circuits, consuming only 45 pJ of active power per spike with a power supply of 0.85 V, can be used as the first stage of processing in low-power artificial chemical sensing devices inspired by natural olfactory systems.

Figure 5: The reciprocal connections between mitral and PGo cells. Spikes from the mitral or PGo cell are sent off-chip by the AER transmitter and routed back to the appropriate axon. The mitral cell is configured so that a “10” type synapse is given a negative weight during synaptic integration. The spike of a PGo cell is routed to its axon in the crossbar which is configured to have a “10” type connection to inhibit the mitral cell. Similarly, the PGo cell is configured so that a “01” type synapse is given a positive weight. The mitral cell axon produces this type of synapse with the PGo cell to excite it.

Mentions:
The internal connections of each glomerular column were implemented by routing the spikes sent out of the core back to axons that connected to the appropriate column of the crossbar. For example, the reciprocal connections between mitral and PGo cells are illustrated in Figure 5. In biological olfactory bulbs, PGo cells short-circuit excitatory currents that are synaptically evoked in a mitral cell and thereby shunt the effects of OSN excitation. However, in our system, neurons only communicate through spikes. We replicated the effects of this shunt inhibition by configuring each mitral cell such that the activity of a spiking inhibitory PGo cell is integrated to shut down the effects of subsequent excitation that the mitral cell receives from the OSNs. The PGo cells were configured such that their spike rates saturated above a certain OSN activation level, ensuring that higher OSN activation levels will overpower PGo inhibition and enable excitation of the mitral cell. Setting the saturation level of the PGo cells is one way in which the degree of contrast enhancement can be adjusted in this circuit.

Figure 5: The reciprocal connections between mitral and PGo cells. Spikes from the mitral or PGo cell are sent off-chip by the AER transmitter and routed back to the appropriate axon. The mitral cell is configured so that a “10” type synapse is given a negative weight during synaptic integration. The spike of a PGo cell is routed to its axon in the crossbar which is configured to have a “10” type connection to inhibit the mitral cell. Similarly, the PGo cell is configured so that a “01” type synapse is given a positive weight. The mitral cell axon produces this type of synapse with the PGo cell to excite it.

Mentions:
The internal connections of each glomerular column were implemented by routing the spikes sent out of the core back to axons that connected to the appropriate column of the crossbar. For example, the reciprocal connections between mitral and PGo cells are illustrated in Figure 5. In biological olfactory bulbs, PGo cells short-circuit excitatory currents that are synaptically evoked in a mitral cell and thereby shunt the effects of OSN excitation. However, in our system, neurons only communicate through spikes. We replicated the effects of this shunt inhibition by configuring each mitral cell such that the activity of a spiking inhibitory PGo cell is integrated to shut down the effects of subsequent excitation that the mitral cell receives from the OSNs. The PGo cells were configured such that their spike rates saturated above a certain OSN activation level, ensuring that higher OSN activation levels will overpower PGo inhibition and enable excitation of the mitral cell. Setting the saturation level of the PGo cells is one way in which the degree of contrast enhancement can be adjusted in this circuit.

Bottom Line:
Our system is based on a digital neuromorphic chip consisting of 256 leaky-integrate-and-fire neurons, 1024 × 256 crossbar synapses, and address-event representation communication circuits.The neural circuits configured in the chip reflect established connections among mitral cells, periglomerular cells, external tufted cells, and superficial short-axon cells within the olfactory bulb, and accept input from convergent sets of sensors configured as olfactory sensory neurons.Our circuits, consuming only 45 pJ of active power per spike with a power supply of 0.85 V, can be used as the first stage of processing in low-power artificial chemical sensing devices inspired by natural olfactory systems.

ABSTRACTWe present a biomimetic system that captures essential functional properties of the glomerular layer of the mammalian olfactory bulb, specifically including its capacity to decorrelate similar odor representations without foreknowledge of the statistical distributions of analyte features. Our system is based on a digital neuromorphic chip consisting of 256 leaky-integrate-and-fire neurons, 1024 × 256 crossbar synapses, and address-event representation communication circuits. The neural circuits configured in the chip reflect established connections among mitral cells, periglomerular cells, external tufted cells, and superficial short-axon cells within the olfactory bulb, and accept input from convergent sets of sensors configured as olfactory sensory neurons. This configuration generates functional transformations comparable to those observed in the glomerular layer of the mammalian olfactory bulb. Our circuits, consuming only 45 pJ of active power per spike with a power supply of 0.85 V, can be used as the first stage of processing in low-power artificial chemical sensing devices inspired by natural olfactory systems.